1. Field of Invention
The invention relates to an antenna, and, in particular, to a flat antenna.
2. Related Art
The rapidly developed radio transmission has brought various products and technologies applied in the field of multi-band transmission, such that many new products have the performance of radio transmission to meet the consumer's requirement. The antenna is an important element for transmitting and receiving electromagnetic wave energy in the radio transmission system. If the antenna is lost, the radio transmission system cannot transmit and receive data. Thus, the antenna plays an indispensable role in the radio transmission system.
In a wireless transmission system, the currently used frequency band specifications include the IEEE 802.11 WLAN (Wireless Local Area Network) and the DECT (Digital Enhanced Cordless Telecommunication) standard. IEEE 802.11 is further divided into the specifications of IEEE 802.11a, IEEE 802.11b and IEEE 802.11g. IEEE 802.11a is the specification corresponding to the frequency band of 5 GHz. IEEE 802.11b and IEEE 802.11g are the specifications corresponding to the frequency band of 2.4 GHz. The DECT standard is the specification corresponding to the frequency band of 1.88 GHz to 1.9 GHz.
To meet the above-mentioned specifications, a flat antenna is frequently used. Referring to FIG. 1, the conventional wireless network device includes a host H1 and two flat antennas 1 and 1′, which are disposed on the host H1 and respectively disposed in casings C1 and C1′. The flat antennas 1 and 1′ have the same specification and operate in the frequency band satisfying the WLAN specification to prevent the single antenna from missing out a portion of a wireless signal when receiving the wireless signal. Thus, the frequently used solution is to use two antennas for the spatial compensation to reduce the missing of the wireless signal.
Similarly, as shown in FIG. 2, a conventional DECT device includes a host H2 and two flat antennas 2 and 2′, which are disposed on the host H2 and respectively disposed in casings C2 and C2′. The flat antennas 2 and 2′ have the same specification and operate in the frequency band satisfying the DECT standard specification. In order to make the signal transmission for the DECT have the spatial compensation effect, two sets of antennas have to be used.
As shown in FIG. 3, if the wireless communication device must have the transmission functions of the WLAN and the DECT, the four flat antennas 1, 1′, 2 and 2′ have to be disposed on a host H3. In other words, the manufacturer has to manufacture the four flat antennas 1, 1′, 2 and 2′ respectively and the manufacturing cost is increased. The flat antennas 1, 1′, 2 and 2′ are assembled on the host H3, and the space is occupied and the too many antennas also influence the glory of the product.
Thus, it is an important subject of the invention to provide a flat antenna, which integrates the transmission functions of the WLAN and the DECT together so as to reduce the number of flat antennas of the communication device.